I've now tried to reproduce the problem on MQ on Windows with the same definitions but on Windows it all works as expected. Incidentally it's MQ V.6.0.1.1 on both the failing Linux environment and on ...
Ok these are the definitions but with the CLWLPRTY set to 9 for the primary and 0 for the failover standby as advised by fjb_saper. The behavior is still the same i.e. an MQPut to Q1 goes to QM1 but a ...